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Ive found this boost anomoly purely by chance and hope some feedback may be able to clear the confusion .
I have a mapped ecu , D4d with egr off . The instructions were to remove the egr vac tube and block it for the egr off function . I believe the egr mil light function and appropriate codes must have been removed in the mapping process however the egr function remains available (as in not deleted) unless the vac tube is disconnected . The remap appeared to be working no problems with significant performance gains but I had no idea of boost figures untill now .
After running this tune with egr vac tube removed and blocked for 2 years now have recently fitted a boost gauge .
It makes 10-12lb max boost and Ive read that factory is approx 15lb .
So it got me thinking about my setup . I reinstalled factory ecu and yep 15-16lb . Put back in my mapped ecu and yep 10-12lb .
Further testing of the mapped ecu , I reconnected the vac hose to egr and boost went up18psi and engine sounds perfect . It really likes the egr vac hose connected .
So Im thinking this can only be one of 2 things .
Either the egr gas is helping somehow with the turbo boosting, or the egr position sensor on top of the egr valve is sending a signal to the ecu which somehow can affect turbo vane angles and boost pressure .
Basically in a nutshell , disconnecting and pluging the egr vac hose is reducing boost level by approximately 40%.
Anyone got any clues ?

Also adding that theres a lot of blanked off egr plates installed in the hilux community which are some full blocks . So Im wondering if the egr supplies the extra pressure into the intake from exhaust backpressure is everyone who has blocked there egr not getting full boost like the scenario Ive described above .
I think it is possible the egr exhaust is flowing in at a higher pressure than the turbo intake boost created and this exhaust pressure lifts total boost .
I dont know Im really only guessing .